On Mon, Jan 24, 2022, at 12:58 AM, Michael Paquier wrote:
> FWIW, I find the API changes of HeapDetermineModifiedColumns() and
> ExtractReplicaIdentity() a bit grotty. Shouldn't we try to flatten
> the old tuple instead? There are things like
> toast_flatten_tuple_to_datum() for this purpose if a tuple satisfies
> HeapTupleHasExternal(), or just heap_copy_tuple_as_datum().
>
I checked v4 and I don't like the HeapDetermineModifiedColumns() and
heap_tuple_attr_equals() changes either. It seems it is hijacking these
functions to something else. I would suggest to change the signature to
static void
heap_tuple_attr_equals(TupleDesc tupdesc, int attrnum,
HeapTuple tup1, HeapTuple tup2,
bool *is_equal, bool *key_has_external);
and
static void
HeapDetermineModifiedColumns(Relation relation, Bitmapset *interesting_cols,
HeapTuple oldtup, HeapTuple newtup,
Bitmapset *modified_attrs, bool *key_has_external);
I didn't figure out a cheap way to check if the key has external value other
than slightly modifying the HeapDetermineModifiedColumns() function and its
subroutine heap_tuple_attr_equals(). As Alvaro said I don't think adding
HeapTupleHasExternal() (as in v3) is a good idea because it does not optimize
genuine cases such as a table whose PK is an integer and contains a single
TOAST column.
Another suggestion is to keep key_changed and add another attribute
(key_has_external) to ExtractReplicaIdentity(). If we need key_changed in the
future we'll have to decompose it again. You also encapsulates that
optimization into the function that helps with future improvements/fixes.
static HeapTuple
ExtractReplicaIdentity(Relation relation, HeapTuple tp, bool key_changed,
bool key_has_external, bool *copy);
--
Euler Taveira
EDB https://www.enterprisedb.com/
